Porous igniter coating for use in automotive airbag inflators

ABSTRACT

An ignition composition effective to form a porous igniter substance capable of adhering to an associated inflator apparatus surface for use in an automotive inflatable restraint system and a method for preparing a porous igniter coating formed from the ignition composition are provided. The ignition composition includes a fuel, an oxidizer, a polymeric binder and a blowing agent effective, upon decomposition, to increase the surface area of the porous igniter substance. The porous igniter substance or coating is formed by heating the ignition composition to a predetermined temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 10/313,819, filed on 6 Dec. 2002. This application is also acontinuation-in-part of U.S. application, Ser. No. 10/359,962 filed on 6Feb. 2003. The co-pending parent applications are hereby incorporated byreference herein in their entirety and are made a part hereof, includingbut not limited to those portions which specifically appear hereinafter.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to an ignition composition foruse in an inflator apparatus for an inflatable restraint system. Moreparticularly, this invention relates to an ignition composition which,upon being heated to a predetermined temperature, forms a porous ignitersubstance which desirably adheres to an associated inflator apparatussurface.

[0003] It is well known to protect a vehicle occupant using a cushion orbag, e.g., an “airbag cushion” that is inflated or expanded with a gaswhen a vehicle experiences a sudden deceleration, such as in the eventof a collision. Such airbag restraint systems typically include: one ormore airbag cushions, housed in an uninflated and folded condition tominimize space requirements; one or more crash sensors mounted on or tothe frame or body of the vehicle to detect sudden deceleration of thevehicle; an activation system electronically triggered by the crashsensors; and an inflator device or apparatus that produces or supplies agas to inflate the airbag cushion. In the event of a sudden decelerationof the vehicle, the crash sensors trigger the activation system which inturn triggers the inflator device which begins to inflate the airbagcushion in a matter of milliseconds.

[0004] Many types of inflator devices have been disclosed in the art foruse in inflating one or more inflatable restraint system airbagcushions. Many prior art inflator devices include a solid form of gasgenerant material which is burned to produce or form gas used in theinflation of an associated airbag cushion.

[0005] Such inflator devices tend to involve a chain of reactions ofmaterials, e.g., pyrotechnics, contained within an inflator device toproduce or generate an inflation medium, e.g., inflation gas, to resultin the deployment of an airbag cushion. For example, such devicescommonly employ a squib or initiator that is electronically ignited whena collision is sensed. The discharge from the squib in turn ignites anignition material or composition generally positioned in close proximityto the squib. The ignition material desirably burns relatively rapidly,with a large caloric output, such as to desirably ignite a supply of gasgenerant material. The gas generant material in turn burns to produce orform gas such as is directed into an associated airbag cushion to effectinflation thereof. In general, the ballistic properties of a gasgenerant material are controlled by the shape (usually tablets orwafers) and burn rate of the gas generant material.

[0006] As will be appreciated, rapid and repeatable ignition of a gasgenerant material is critical to providing inflator devices that enablean airbag cushion to reliably deploy in the very short period of timeassociated with vehicle occupant passive restraint systems. For example,inflator designers typically require the period of time followingactivation of the system until gas is expelled from an inflator to beless than 3 milliseconds.

[0007] Inflator designs that attempt to incorporate, by simple blendingor mixing together, an igniter powder with gas generant tablets, wafersor other gas generant particle shapes have generally not provensuccessful. In particular, igniter powders in such inflator designs tendto be susceptible to migration away for the squib and gas generantparticles over time. Consequently, such designs may experienceunacceptable delays and produce or result in less than optimal occupantprotection.

[0008] In view thereof, conventional inflator devices have commonlyincluded some form of ignition material packaging to ensure properplacement and positioning of the ignition material within the inflatordevice to effect desired ignition and reaction of the associated gasgenerant material. More specifically, it is common for inflator devicesto include a powdered ignition material that is packaged within aseparate container in close proximity to the squib and the gas generantparticles. In such an arrangement, the squib is able to rapidly ignitethe ignition powder which in turn causes the rapid ignition of the gasgenerant material.

[0009] In practice, the packaging of such ignition materials can berelatively simple and straightforward such as by packaging the ignitionmaterial in a small canister, such as an aluminum canister, in thecenter of a toroidal-shaped driver inflator or relatively complex suchas by packaging the ignition material in a tubular device which in turnis inserted down a bore of a stack of gas generant wafers in typical,cylinder-shaped passenger inflator device. Regardless of the specificsof such designs, the packaging of a powder ignition material within aninflator device has typically required the inclusion of additional partsand added weight.

[0010] As will be appreciated, space is often at a premium in modernvehicle designs. Consequently, it is generally desired that the spacerequirements for various vehicular components, including inflatablevehicle occupant restraint systems, be reduced or minimized to as greatan extent as possible. The incorporation of an igniter assembly such asdescribed above and associated support structure(s), may require alarger than desired volume of space within an associated inflatordevice. In particular, such volume of space could alternativelypotentially be utilized to store or contain gas generant material, andthereby permit the volume of space required by the inflator device to bereduced.

[0011] In addition, the incorporation and use of an ignition assemblyand process such as described above, can detrimentally impact either orboth the weight and cost of the corresponding apparatus hardware.

[0012] Thus, there is a need and a demand for alternative airbaginflator device ignition schemes and, in particular, a need and a demandfor avoiding the requirement or inclusion of separate ignitioncomposition charges housed in associated hardware.

[0013] In an alternative approach, an ignition composition has beenpressed into a particle shape with similar dimensions as the gasgenerant particles and to strategically position these igniter particleswithin the gas generant mass in close proximity to the squib. Specificexamples of this approach include: ignition material wafers placed orpositioned at the end of a gas generant wafer stack next to a squib orplaced with periodicity along the length of a gas generant wafer stack;ignition material tablet(s) placed or positioned at the squib end of abed of gas generant tablets in a side impact inflator; ignition materialtablets placed down the bore of a gas generant wafer stack; ignitionmaterial tablets placed in the center of a bed of gas generant tabletsin a toroidal driver inflator; or similar concepts. Unfortunately,pressed ignition particles typically present a greatly reduced surfacearea as compared to a similar mass of ignition powder. As will beappreciated, a reduced surface area of the ignition material duringcombustion will typically result in a reduced rate of energy release andmay, thus, cause or result in undesired delays within an airbag inflatordevice.

[0014] Thus, is also a need and a demand for ignition materials having asurface area similar to those of powdered ignition materials.

[0015] In another approach, an ignition composition may be applied orcoated onto a surface of an inflator apparatus such as, for example, ona surface of a gas generant material, on an interior surface of aninflator device, on a surface of an electrical squib, on a surface of adamper pad, or combinations thereof. For example, Mendenhall et al.,U.S. Pat. No. 6,077,372 issued Jun. 20, 2000 discloses an ignitionenhanced gas generant formulation and method of making the sameutilizing a solvent effective to partially solubilize at least onecomponent of each of a selected ignition composition, and uponapplication to the gas generant, at least one component of an associatedgas generant. Parkinson et al., U.S. Pat. No. 6,527,297 issued Mar. 2,2003 discloses applying an ignition composition including a siliconeresin additive effective to adhere the ignition composition to inflatorapparatus surfaces such as damper pads.

[0016] While such ignition composition coatings may be effective inovercoming or minimizing various shortfalls of prior ignition assembliesand processes, further particular improvements have been sought anddesired. For example, it is generally desired that a coating of ignitionmaterial strongly adhere to an associated inflator apparatus surfacesuch that the ignition material does not readily or easily separate fromthe surface either during handling or when subjected to normal vibrationsuch as may be experienced by an inflator device during its lifetime inan automotive vehicle. Increasing the adhesion of the ignition materialcan be accomplished by incorporating a soluble polymeric binder materialinto a slurried ignition composition that upon drying forms a film thatimparts a cohesiveness to the ignition material and an adhesive physicalbond to an associated surface. The degree of adhesion is generallydirectly proportional to the level of polymeric material in the ignitioncomposition. However, a decrease in performance of the ignitionmaterial, as manifested by an increased delay ignition of the ignitermaterial, has been observed as the level of polymeric material isincreased in the ignition composition. It is believed that such loss ofperformance is likely attributable to a reduction of igniter materialsurface area resulting in a loss of mass burning rate.

[0017] Thus, there is a further need and a demand for an ignitionmaterial that not only desirably adheres to an associated inflatorapparatus surface but also has or provides a desirably large surfacearea.

SUMMARY OF THE INVENTION

[0018] A general objective of the invention is to provide an improvedignition composition. A more particular objective is to provide such anignition composition which forms a porous igniter substance having adesirably large or increased surface area. In particular the inventionis directed to providing an ignition composition which may be used toform a porous igniter substance capable of adhering to an associatedinflator apparatus surface.

[0019] A more specific objective of the invention is to overcome one ormore of the problems described above.

[0020] The general object of the invention can be attained, at least inpart, through an ignition composition effective to form an ignitersubstance having a surface area, the ignition composition including afuel, an oxidizer, a polymeric binder and blowing agent effective, upondecomposition, to increase the surface area of the igniter substance,wherein the ignition composition, upon being heated to a predeterminedtemperature, forms an igniter substance which is porous and capable ofadhering to an associated inflator apparatus surface. In accordance withthe invention, the associated inflator apparatus surface mayalternatively include at least a portion of a gas generant wafer ortablet, at least a portion of an interior surface of the inflator devicesuch as the inner surface of a hybrid gas storage container, at least aportion of an electrical squib, at least a portion of a surface of adamper pad, and combinations thereof.

[0021] The prior art generally fails to provide an ignition compositionwhich may be used to form an igniter substance having a desirably largeor increased surface area and which igniter substance readily adheres toan associated inflator apparatus surface such as to form a porouscoating thereon.

[0022] The invention further comprehends an ignition compositioneffective to form an igniter substance, the ignition compositionincluding:

[0023] about 15 to about 50 composition weight percent of a fuel;

[0024] about 50 to about 85 composition weight percent of an oxidizer;

[0025] about 1 to about 20 composition weight percent of a polymericbinder; and

[0026] about 1 to about 20 composition weight percent of a blowing agenteffective, upon decomposition, to increase the surface area of theigniter substance,

[0027] wherein the ignition composition, upon being heated to apredetermined temperature, forms an igniter substance which is porousand capable of adhering to an associated inflator apparatus surface.

[0028] The invention still further comprehends, in accordance with onepreferred embodiment, a gas generant material for use in an automotivesafety restraint system including a porous igniter coating that adheresto at least a portion of a surface of the gas generant material. Inaccordance with another preferred embodiment, the invention furthercomprehends a hybrid gas storage container including a porous ignitercoating adhered to an inner surface of the container. The inventionstill further comprehends, in accordance with yet another preferredembodiment, a damper pad for use in automotive safety restraint systemincluding a porous igniter coating adhered to at least a portion of asurface of the pad.

[0029] Other objects and advantages will be apparent to those skilled inthe art from the following detailed description taken in conjunctionwith the appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a cross-section view of a coated gas generant materialincluding a porous igniter coating adhered to at least a portion of aselected surface of a gas generant material, in accordance with oneembodiment of the invention.

[0031]FIG. 2 is a side-sectional view of a single stage hybrid inflatordevice including a porous igniter coating adhered to an interiorsurface, in accordance with one embodiment of the invention.

[0032]FIG. 3 is a side sectional view of a single stage inflator deviceincluding a damper pad cushion including a porous igniter coatingadhered to at least a portion of a surface of the pad, in accordancewith one embodiment of the invention.

[0033]FIG. 4 is a graphical depiction of combustion chamber pressure asa function of time performance realized with a test inflator in Example1 and Comparative Example 1, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention provides an ignition composition effectiveto form an igniter substance desirable for use in an inflator device ofan inflatable restraint system. More particularly, the present inventionprovides an ignition composition which may be used to form an ignitersubstance which is not only capable of adhering to an associatedinflator apparatus surface but which also has a desirably large orincreased surface area.

[0035] In accordance with the invention, an ignition compositionincludes: a fuel; an oxidizer; a polymeric binder; and a blowing agent.Generally, upon being heated to a predetermined temperature, theignition composition forms an igniter substance that is porous andcapable of adhering to an associated inflator apparatus surface. Theblowing agent is generally effective, upon decomposition, to suitablyincrease the surface area of the igniter substance.

[0036] Those skilled in the art and guided by the teachings hereinprovided will appreciate that the invention can desirably be applied orpractice in conjunction with various ignition formulations such as mayfind application in inflatable restraint systems. In particular, theinvention desirably can be applied to various igniter formulations suchas incorporate or em ploy a selected fuel and oxidizer.

[0037] For example, suitable fuel materials in accordance with certainpreferred embodiments of the invention include one or more metals, metalhydrides, metalloids, gas producing organic compounds, gas producinginorganic compounds, and polymeric binders. In accordance with certainpreferred embodiments, it is desirable that the fuel material employedin the ignition composition be in the form of a finely dividedparticulate or a powdered material. Suitable metal fuels for use in theinvention include, but are not limited to, aluminum, magnesium, alloysof aluminum and magnesium, and combinations thereof. In accordance withcertain preferred embodiments, the fuel desirably is an alloy ofaluminum and magnesium. Examples of suitable metalloids for use in thepractice of the invention include, but are not limited to, boron,silicon and the like. A suitable gas producing organic compound inaccordance with certain preferred embodiments of the invention isguanidine nitrate.

[0038] Typically, the ignition composition of the invention contains anamount of fuel effective to result in efficient ignition of anassociated gas generant material. More particularly, the ignitioncomposition of the invention typically includes about 15 to about 50composition weight percent of a fuel.

[0039] Suitable oxidizer materials in accordance with certain preferredembodiments of the invention include one or more alkali and alkalineearth metal nitrites, nitrates, chlorates, and perchlorates, ammoniumnitrate, ammonium perchlorate, transition metal oxides, hydroxide,carbonates, nitrates, and perchlorates, and transition metal complexnitrates, nitrites, and perchlorates, and fluoropolymers, for example.In accordance with certain preferred embodiments of the invention, theignition composition contains potassium nitrate oxidizer. Generally, inthe practice of the invention, the ignition composition includes about50 to about 85 composition weight percent oxidizer.

[0040] As identified above, the ignition composition of the inventionalso desirably includes a polymeric binder. The polymeric binderdesirably imparts adhesive properties to the ignition compositioneffective to adhere an igniter substance formed by or resulting from thesubject ignition composition to an associated surface such as aninflator apparatus surface.

[0041] Various polymeric binder materials have been found to be suitablefor use in the ignition compositions of the present inventions. Examplesof suitable polymeric binders include, but are not limited to, modifiedcellulose polymers such as, for example, hydroxypropyl cellulose,acrylate polymers such as, for example, polyacrylate polymers,acrylamide polymers, and combinations thereof. In accordance withcertain preferred embodiments, the ignition composition includeshydroxypropyl cellulose polymeric binder. In accordance with anotherpreferred embodiment of the invention, the ignition compositionadvantageously includes a polymeric binder containing an aqueousemulsion of polyacrylate polymers. In particular, modified cellulosepolymer and polyacrylate polymer binders can advantageously be utilizedin accordance with the present invention at least in part due to theirsolubility in environmentally friendly solvents which dry rapidly suchas, for example, alcohols. Polyacrylate polymeric binders canadvantageously be utilized in certain embodiments of the invention atleast in part due to their desirable level of adhesion to selectsurfaces and durability when exposed to vibrational energy.

[0042] Desirably, the amount of polymeric binder included in theignition composition is selected to achieve an acceptable level ofadhesion with an associated inflator apparatus surface. Advantageously,the ignition composition includes about 1 to about 20 composition weightpercent of polymeric binder.

[0043] The ignition composition of the invention further includes ablowing agent. Suitable blowing agents for use in the practice of theinvention generally include those blowing agent materials that decomposeto gaseous species when subjected to heat. In practice, those blowingagents that at least partially decompose into gas at temperatures belowthe autoignition temperature of the ignition composition are preferred.Typically, such decomposition temperatures are less than 350° C. suchthat the ignition composition is required to only be heated totemperatures below 350° C. in order to effect decomposition of theincluded blowing agent. Those blowing agents that decompose attemperatures between about 100° C. and 300° C. are believed to be mostuseful and desirable in the practice of the invention.

[0044] For certain desired embodiments, such as when an ignitioncomposition in accordance with the invention is applied to at least aportion of a surface a gas generant tablet or wafer, the ignitioncomposition typically includes a blowing agent that decomposes at atemperature less than the autoignition temperature of the gas generanttablet or wafer. Typically, those blowing agents that decompose attemperatures below about 200° C. are believed to be most useful anddesirable in the practice of such embodiments.

[0045] Furthermore, while the use of a blowing agent that decomposesinto all gaseous species is generally preferred, the broader practice ofthe invention is not necessarily so limited, provided, that anyresulting solid decomposition products do not substantially inhibitcombustion of the ignition composition or are otherwise detrimental tooperation or use of such compositions or devices which include suchcompositions. Examples of useful blowing agents that typically produceor result in only gaseous products include: aminoguanidine bicarbonate,ammonium oxalate, azodicarbonamide, ammonium carbonate, ammoniumcarbamate, ammonium bicarbonate, 4,4′-oxydibenzene hydrazide, p-toluenesulfonyl semicarbazide and organic acids. Additional useful blowingagents that generally decompose leaving some solids include: alkali andalkaline earth metal carbonates or bicarbonates, such as basic coppercarbonate, metal ammine carbonates such as copper diammine carbonate,and metal ammine salts of organic acids such as copper diammine oxalate,and metal salts of organic acids, for example. In accordance withcertain preferred embodiments, the blowing agent included in theignition composition is aminoguanidine bicarbonate.

[0046] In general, the invention can desirably be practiced such thatthe ignition composition includes about 1 to about 20 composition weightpercent of a blowing agent.

[0047] In addition, ignition compositions in accordance with theinvention may advantageously contain or include one or moredesensitizing agents such as to desirably desensitize the ignitersubstance to the effects of one or more stimuli such as friction, impactand electrostatic discharge, for example. Suitable desensitizing agentsfor use in the practice of the invention include, but are not limitedto, bentonite clay, silicon dioxide, aluminum oxide, zirconium oxide,titanium oxide, and mixtures thereof. In accordance with certainpreferred embodiments, bentonite clay is included in the ignitioncomposition as a desensitizing agent. Advantageously, the ignitioncomposition may include a desensitizing agent in an amount of up toabout 10 composition weight percent.

[0048] The invention further comprehends a method for preparing anigniter substance containing the ignition composition as disclosedabove. In particular, in accordance with certain preferred embodiments,an igniter substance can be formed by heating an ignition composition ofthe invention, as described above, to a predetermined temperatureeffective to at least partially decompose the blowing agent therebyincreasing the surface area of the igniter substance by rendering itporous. Generally, the ignition composition can be heated to apredetermined temperature of between about 100° C. and about 200° C.,such as between about 130° C. and about 170° C., to at least partiallydecompose the blowing agent and render the resulting igniter substanceporous.

[0049] In accordance with one preferred embodiment of the invention, theignition composition is prepared by stirring a blend of dry componentsincluding a fuel, an oxidizer and a blowing agent into a polymersolution, including a polymeric binder dissolved in a carrier solventsuch as, for example, acetone, to form a slurry. The ignitioncomposition slurry is then suitably applied to an associated inflatorapparatus surface such as by spraying, dipping, rolling, brushing or thelike. The ignition composition slurry is then heated to a predeterminedtemperature to form an igniter substance which is porous and capable ofadhering to an associated inflator apparatus surface such as, forexample, at least a portion of a surface of a gas generant wafer ortablet, at least a portion of an interior surface of an inflator device,at least a portion of a surface of an electrical squib, and/or at leasta portion of a surface of a damper pad.

[0050] As will be appreciated by one of skill in the art and guided bythe teachings herein provided, the ignition composition of the presentinvention can be utilized in a variety of inflator device in a varietyof manners. For example, an ignition composition as disclosed above maybe used to form a porous igniter coating adhered to at least a portionof a surface of a gas generant wafer or tablet.

[0051] Referring to FIG. 1, a coated gas generant material, generallydesignated by reference numeral 110, includes an ignition compositionapplied to at least a portion of a surface 112 of a gas generant tablet114. The ignition composition, upon heating to a predeterminedtemperature, forms a porous igniter coating 116 adhered to at least aportion of the surface 112 of the gas generant tablet 114. When ignited,the porous igniter coating 116 causes or results in ignition of the gasgenerant tablet 114.

[0052] As will be appreciated by one of skill in the art and guided bythe teachings herein provided, the intimate, direct contact of theporous igniter coating 116 with the gas generant tablet 114 is desirablefor efficient ignition of the gas generant material. Such efficiency, inpractice, can favorably reduce performance variability in an associateinflator device (not shown).

[0053] In accordance with another preferred embodiment of the invention,an ignition composition as disclosed above may be utilized to form aporous igniter coating adhered to an inner surface of a hybrid inflatorgas storage container. For example, referring to FIG. 2, a hybridinflator device, generally designated by reference numeral 210, includesan ignition composition of the invention applied to at least a portionof at least one interior surface thereof.

[0054] The hybrid inflator assembly 210 includes a pressure vessel 212including a storage chamber 214. The storage chamber 214 is filled andpressurized with an inert gas such as, for example, argon, helium ornitrogen, or a reactive gas such as, for example, nitrous oxide to apressure typically in the range of about 2000 psi to about 4000 psi. Thehybrid inflator assembly also includes a diffuser 216 and an igniterassembly 218, such as may desirably be appropriately joined or fastenedtogether. The diffuser 216 includes a burst disk 240 which serves toseal the gases contained in the storage chamber 214 from the diffuser216.

[0055] The hybrid inflator assembly 210 further includes a fill port 220used for gas pressurization, which is integral to the pressure vessel212 and which, after pressurization, is appropriately sealed such aswith a ball weld 222.

[0056] The hybrid inflator assembly 210 additionally includes a porousigniter coating 224 in contact with at least a portion of the interiorof the pressure vessel 212. In practice and such as described above, anignition composition in accordance with the invention is desirablyapplied to at least a portion of a selected interior surface of thepressure vessel 212 and thereafter heated to predetermined temperatureto form the porous igniter coating 224.

[0057] The igniter assembly 218 includes an igniter squib 226 and asquib adapter or holder 228. Suitably, the squib adapter 228 is mountedto or mated with the igniter assembly 218 via a mounting opening 230.Also included in the igniter assembly 218 is a pyrotechnic charge 232housed within a container 234 adjacent to an orifice 236, which issealed by a burst disk 238 attached to the igniter assembly 218.

[0058] When actuated, the igniter squib 226 ignites the pyrotechniccharge 232 contained within the container 234. The pyrotechnic charge232 produces reaction products including a hot flame and gas in aquantity sufficient to burst the container 234 and the burst disk 238.The released gas and hot flame travel through the orifice 236 causingignition of the porous igniter coating 224. The products formed orresulting from such ignition are brought, through the designedconfiguration, in direct contact with the gas or gases contained in thestorage chamber 214. The subsequent heating of these gases raises thepressure inside the storage chamber 214 to a level sufficient to breakthe burst disk 240. The heated gases are thereby released into thediffuser 216 and pass out of the hybrid inflator assembly 210 into anassociated airbag cushion (not shown).

[0059] As will be appreciated by one of skill in the art and guided bythe teachings herein, the hybrid inflator assembly 210 eliminates theneed for gas heater assembly elements such as a gas generant cup andassociated hardware. Such elimination, in practice, can favorably reduceone or more of assembly weight and size as well as improve performancedependability and thus significantly alter, i.e., reduce, costs such asassociated with inflator assembly manufacture, installation and/oroperation, for example.

[0060] In accordance with an additional preferred embodiment, anignition composition as disclosed above may be utilized to form a porousigniter coating adhered to at least a portion of a surface of a damperpad. For example, referring to FIG. 3, a single stage inflator device310 has a generally cylindrical external outline and includes a housing312 such as formed from two structural components, i.e., a lower shellor base portion 314 and an upper shell or diffuser cap portion 316, suchas may desirably be appropriately joined or fastened together.

[0061] The housing 312 is configured to define a generally cylindricalchamber, here designated by reference numeral 318. The chamber 318contains or houses a supply of gas generant material 320, such ascomposed of a pyrotechnic, such as is known in the art, in a desiredselected form. A filter assembly 322 surrounds the gas generant material320.

[0062] The inflator device 310 includes a retainer 324, a diffuserdamper pad cushion 326 and a base damper pad cushion 328 which serve toprevent undesired rattle or contact of the gas generant material 320within the inflator device 310. In practice and such as described above,the diffuser damper pad cushion 326 and/or the base damper pad cushion328 can be treated with an igniter composition as described above thathas been heated to a predetermined temperature to form a porous ignitercoating on at least a portion of a surface of the damper pad(s). Forexample, damper pad cushion 326 can include a porous igniter coating 330adhered to at least a portion of a surface of the pad.

[0063] The inflator device 310 further includes an igniter assembly,generally designated by reference numeral 332 such as in the form of anigniter squib 334 and a squib adapter or holder 336. Suitably, theigniter squib 334 is mounted to or mated with the housing 312 in alocation within the chamber 318 via a mounting opening 338.

[0064] When actuated, the squib 334 causes ignition of the porousigniter coating 332 of the diffuser damper pad cushion 326. The productsformed or resulting for such ignition are, through the designedconfiguration, in direct contact with the gas generant material 320contained within the chamber 318 such as to result in the ignition andreaction of the gas generant material 320. The gases produced or formedby such reaction then passes out of the inflator device 310 into anassociated airbag cushion (not shown).

[0065] As will be appreciated, the inflator assembly 310 eliminates theneed for assembly elements such as an igniter cup and/or an igniter tubeto house or contain the igniter substance. Such elimination, inpractice, can favorably reduce assembly weight, size and/or performancedependability and thus significantly alter, i.e., reduce, costs such asassociated with the inflator assembly manufacture, installation and/oroperation, for example.

[0066] The present invention is described in further detail inconnection with the following examples which illustrate or simulatevarious aspects involved in the practice of the invention. It is to beunderstood that all changes that come within the spirit of the inventionare desired to be protected and thus the invention is not to beconstrued as limited by these examples.

EXAMPLES

[0067] An ignition composition (Example 1) in accordance with theinvention and as shown in TABLE 1, below, was prepared by dissolvinghydroxypropyl cellulose polymeric binder in a carrier solvent to form apolymer solution. Dry ingredients including a fuel containing boron anda 50/50 aluminum/magnesium alloy, potassium nitrate oxidizer andbentonite clay desensitizing agent and aminoguanidine bicarbonate weremixed to form a precursor blend. The precursor blend was thoroughlymixed into the polymer solution to form an ignition composition slurry.The ignition slurry was sprayed onto the surface of a standard gasgenerant table having a diameter of 0.25 inch (0.64 cm) and a thicknessof 0.070 inch (0.18 cm) in a tumble coating apparatus at a 2.0 wt %level (after heating). The coated gas generant tablets were dried atapproximately 140° C. to remove the carrier solvent, decompose theblowing agent present in the ignition composition and, in accordancewith the invention, form a porous igniter coating on the gas generanttablets.

[0068] A comparative ignition composition (Comparative Example 1, “CE1”) as shown in TABLE 1, below was prepared in the same manner, however,without the aminoguanidine bicarbonate blowing agent. The comparativeignition slurry was sprayed onto the surface of a standard gas generanttablet having a diameter of 0.25 inch (0.64 cm) and a thickness of 0.70inch (0.18 cm) in a tumble coating apparatus at a 2.0 wt % level (afterheating). The coated gas generant tablets were dried at approximately140° C. to remove the carrier solvent and form a comparative ignitercoating on the gas generant tablets. After heating, the porous ignitercoating in accordance with invention (Example 1) and the comparativeigniter coating (CE 1) had the same composition. TABLE 1 Composition Wt.% Ingredient Example 1 CE 1 50/50 Al/Mg alloy Fuel 11.6 12.9 Boron Fuel11.3 12.5 Potassium nitrate Oxidizer 57.7 64.1 Hydroxypropyl cellulosePolymeric binder 2.7 3.0 Aminoguanidine Blowing agent 10.0 0.0bicarbonate Bentonite clay Desensitizing agent 6.7 7.5 TOTAL 100.0 100.0

[0069] The coated gas generant materials of Example 1 and ComparativeExample 1 were each tested to determine the level of coating retentionby in each case loading 80 grams of the respective coated gas generanttablets onto a 25 mesh screen and then subjecting the coated gasgenerant tablets in each case to vibration for five minutes. The coatedgas generant tablets were weighed before and after vibration in eachcase and the loss of igniter coating was calculated for each sample.TABLE 2, below, reports the results in terms of percentage retention ofthe igniter coating for each sample.

[0070] The coated gas generant materials of Example 1 and ComparativeExample 1 were each also tested to determine the level of performance asmanifested by delay in ignition by loading 32 grams of the respectivecoated gas generant tablets into a test inflator device. The testinflator device in each case was mated to a 100 liter tank equipped witha pressure transducer to measure the pressure within the tank. The testinflator device was also provided with a pressure transducer to measurepressure within the combustion chamber of the test inflator device. Thetest inflator device in each case was fired into the tank and combustionchamber pressure vs. time performance was recorded by means of a datacollection system. The period of time until a first indication ofpressure in the pressure vs. time curve is the delay reported in TABLE2, below. The pressure vs. time performance curves collected for eachsample are shown in FIG. 4. TABLE 2 Sample /Retention Delay(milliseconds) Example 1 96.77 1 CE 1 95.80 3

[0071] The data in TABLE 2 shows that the porous igniter coating formedfrom an ignition composition in accordance with the invention(Example 1) demonstrated at least comparable and slightly improvedadhesion to the gas generant surface over the igniter coating formedfrom a comparable ignition composition prepared without a blowing agent(CE 1).

[0072] The data in TABLE 2 also shows that the porous igniter coatingformed from an ignition composition in accordance with the invention(Example 1) demonstrated a significantly decreased delay in ignitionand, therefore an improvement in performance, over the igniter coatingformed form a comparable ignition composition prepared without a blowingagent (CE 1).

[0073] As discussed above, while it may be desirable to increase theextent of adhesion of an ignition material to a selected surface inorder to reduce or prevent undesirable loss of the ignition materialfrom the surface and the extent of ignition material adhesion cantypically be improved by including a polymeric binder in the ignitioncomposition, such an increase in the polymer content of an ignitioncomposition normally has associated with it a decrease in performance asmanifested by delay in ignition.

[0074] Referring to the combustion pressure vs. time curve shown in FIG.4, the graph shows that from the point of firing (Time=0) to the pointof a first indication of pressure approximately 1 millisecond elapsedfor Example 1 whereas for Comparative Example (CE 1) nearly 3milliseconds elapsed. Thus, as shown in TABLE 2 and FIG. 4, the loss ofperformance typically observed when the polymeric binder concentrationof an ignition composition is increased can desirably be offset inaccordance with the invention by increasing the surface area of theigniter coating such as by including a blowing agent in the associatedignition composition.

[0075] Thus, the invention provides an improved ignition compositionwhich forms a porous igniter substance having a desirably large orincreased surface area. In particular, the invention provides animproved ignition composition which may be used to form a porous ignitersubstance capable of adhering to an associated inflator apparatussurface.

[0076] The invention illustratively disclosed herein suitably may bepracticed in the absence of any element, part, step, component, oringredient which is not specifically disclosed herein.

[0077] While in the foregoing detailed description this invention hasbeen described in relation to certain preferred embodiments thereof, andmany details have been set forth for purposes of illustration, it willbe apparent to those skilled in the art that the invention issusceptible to additional embodiments and that certain of the detailsdescribed herein can be varied considerably without departing from thebasic principles of the invention.

What is claimed is:
 1. An ignition composition effective to form anigniter substance having a surface area, the ignition compositionincluding a fuel and an oxidizer and further comprising: a polymericbinder; and a blowing agent effective, upon decomposition, to increasethe surface area of the igniter substance; wherein the ignitioncomposition, upon being heated to a predetermined temperature, forms anigniter substance which is porous and capable of adhering to anassociated inflator apparatus surface.
 2. The ignition composition ofclaim 1, wherein the fuel comprises a powdered metal.
 3. The ignitioncomposition of claim 1, wherein the fuel is selected from the groupconsisting of aluminum, magnesium, alloys of aluminum and magnesium, andcombinations thereof.
 4. The ignition composition of claim 1, whereinthe fuel comprises an alloy of aluminum and magnesium.
 5. The ignitioncomposition of claim 1, wherein the fuel comprises a metalloid.
 6. Theignition composition of claim 1, wherein the fuel comprises boron. 7.The ignition composition of claim 1, wherein the fuel comprises a gasproducing organic compound.
 8. The ignition composition of claim 1,wherein the fuel comprises guanidine nitrate.
 9. The ignitioncomposition of claim 1, wherein the polymeric binder is selected fromthe group consisting of modified cellulose polymers, acrylate polymers,acrylamide polymers, and combinations thereof.
 10. The ignitioncomposition of claim 1, wherein the polymeric binder comprises amodified cellulose polymer including hydroxypropyl cellulose.
 11. Theignition composition of claim 1, wherein the blowing agent is selectedfrom the group consisting of aminoguanidine bicarbonate, ammoniumoxalate, azodicarbonamide, ammonium carbonate, ammonium carbamate,ammonium bicarbonate, 4,4′-oxydibenzene sulfonyl hydrazide, andcombinations thereof.
 12. The ignition composition of claim 1, whereinthe blowing agent comprises aminoguanidine bicarbonate.
 13. The ignitioncomposition of claim 1, wherein the ignition composition upon beingheated to a temperature of between about 130° C. and about 170° C. formsthe porous igniter substance.
 14. The ignition composition of claim 1,wherein the associated surface is selected from the group consisting ofat least a portion of a surface of a gas generant wafer or tablet, atleast a portion of an interior surface of an inflator device, at least aportion of a surface of an electrical squib, at least a portion of asurface of a damper pad, and combinations thereof.
 15. A gas generantmaterial for use in an automotive safety restraint system comprising:the ignition composition of claim 1 applied to at least a portion of asurface of the gas generant material; wherein the ignition composition,upon being heated to a predetermined temperature, forms a porous ignitercoating that adheres to at least a portion of the surface of the gasgenerant material.
 16. A hybrid gas storage container for use in anautomotive safety restraint system comprising: the ignition compositionof claim 1 applied to an inner surface of the hybrid gas storagecontainer; wherein the ignition composition, upon being heated to apredetermined temperature, forms a porous igniter coating that adheresto the inner surface of the hybrid gas storage container.
 17. A damperpad for use in an automotive safety restraint system comprising: theignition composition of claim 1 applied to at least a portion of asurface thereof; wherein the ignition composition, upon being heated toa predetermined temperature, forms a porous igniter coating that adheresto at least a portion of the surface of the damper pad.
 18. An ignitioncomposition effective to form an igniter substance having a surfacearea, the ignition composition comprising: about 15 to about 50composition weight percent of a fuel; about 50 to about 85 compositionweight percent of an oxidizer; about 1 to about 20 composition weightpercent of a polymeric binder; and about 1 to about 20 compositionweight percent of a blowing agent effective, upon decomposition, toincrease the surface area of the igniter substance; wherein the ignitioncomposition, upon being heated to a predetermined temperature, forms anigniter substance which is porous and capable of adhering to anassociated inflator apparatus surface.
 19. The ignition composition ofclaim 18, wherein the fuel is selected from the group consisting ofmetal fuels, metalloid fuels, gas generating organic fuels, andcombinations thereof.
 20. The ignition composition fo claim 18, whereinthe fuel comprises a metal fuel selected from the group consisting ofaluminum, magnesium, alloys of aluminum and magnesium, and combinationsthereof.
 21. The ignition composition of claim 18, wherein the fuelcomprises an alloy of aluminum and magnesium.
 22. The ignitioncomposition of claim 21, wherein the fuel further comprises boron. 23.The ignition composition of claim 18, wherein the oxidizer is potassiumnitrate.
 24. The ignition composition of claim 18, wherein the polymericbinder is hydroxypropyl cellulose.
 25. The ignition composition of claim18, wherein the polymeric binder is an aqueous emulsion of polyacrylatepolymers.
 26. The ignition composition of claim 18, wherein the blowingagent is aminoguanidine bicarbonate.
 27. The ignition composition ofclaim 18, further comprising a desensitizing agent.
 28. The ignitioncomposition of claim 26, wherein the ignition composition comprises adesensitizing agent in an amount of up to about 10 composition weightpercent.
 29. The ignition composition of claim 27, wherein thedesensitizing agent is bentonite clay.